1. Field of the Invention
Polycarbonates are distinguished by high strength and toughness. However, the stress cracking resistance of moldings produced from pure polycarbonates is not satisfactory. For this reason, blends of polycarbonates with poly(alkylene terephthalates) are frequently employed in industry as disclosed, for example, in DE-OS 1,694,124.
2. Description of the Background
In industry, the comparatively low low-temperature impact strength of polycarbonates is regarded as unsatisfactory. For this reason, there is interest in molding compositions which contain, besides polycarbonates and, if appropriate, poly(alkylene terephthalates), additional components which improve the low-temperature impact strength. Thus, for example, the addition of acrylonitrile-butadiene-styrene copolymers to polycarbonates is described in U.S. Pat. No. 4,172,103. Further, improvement in the impact strength through addition of polyether esters is revealed in EP-OS 0,150,454.
It has been proposed to improve the impact strength of moldings based on polycarbonates by selectively adding hydrogenated styrene-diene block copolymers to polycarbonates. In addition, U.S. Pat. No. 4,320,212 discloses acrylate copolymers as impact modifying additives for polycarbonate molding compositions. Further, it is known that the impact strength of polycarbonates can be improved by the added presence of copolymers based on ethylene and unsaturated functionalized monomers (cf. DE-OS 3,004,942, DE-OS 3,234,174, EP-OS 0,020,605 and EP-SO 0,106,027). Finally, the notched impact strength of polycarbonates is also increased by the added presence of functionalized rubbers (cf. DE-OS 2,343,609, JP-OSS 82/92,045 and 83/136,652).
However, the known mixtures do not exhibit satisfactory low-temperature notched impact strength (cf. EP-OS 0,106,027). In a number of cases, the impact modifying component is difficult to disperse in the polymer matrix. If high energy is employed to improve distribution of the impact modifying component, thermal damage to the polymer matrix cannot be excluded.
Molding compositions which contain polymers having a glass transition temperature lower than -20.degree. C. in addition to polycarbonates and poly(alkylene terephthalates) can be processed to form moldings having a low tendency to warp. However, this does not improve the impact strength (cf. DE-OS 3,118,697). For this reason, it would not be apparent to one skilled in the art to employ polyoctenylenes whose glass transition temperature is -80.degree. C. as impact modifiers in polycarbonate compositions. Further, there are doubts as to the compatibility and dispersibility of the two polymers. This is because experiments have shown that, in the customary process for the production of molding compositions based on polycarbonates, polyoctenylenes do not improve, but, in contrast, even slightly impair, the impact strength at room temperature. This surely does not lead one skilled in the art to consider polyoctenylenes as impact modifiers. A need therefore continues to exist for a polycarbonate composition of improved impact strength properties.